Currently ceramic substrates are used as substrates for modules and as system carriers for whole circuit architectures that replace the plastic circuit boards. Ceramic substrates have the advantage that they are mechanically stable, are produced by micromechanical structuring techniques and also can be mounted with un-housed components. In addition, ceramic, multilayer substrates are known, for which metallization planes, in which passive components and wiring structures can be implemented by structuring, are provided between dielectric, ceramic layers. In addition, methods are known for encapsulating ceramic module or system carriers hermetically with the components applied thereon. Due to the high density of the ceramic substrates, these encapsulated modules have a high imperviousness with respect to gases and moisture.
The mounting of components onto ceramic substrates can take place by different bonding techniques. For example, SMD-methods, flip-chip arrays and wire bond techniques are known. The two latter methods can be implemented with unhoused components, so-called “bare dies.” In both cases, it is necessary to make available bondable metallic surfaces on the ceramic substrate. For populating the ceramic substrate with the components in a high speed automation system within a production line, strict requirements are placed on the smoothness of the bond surface. The problem in this case is that the bond surfaces used heretofore for ceramic substrates do not satisfy these requirements. Formerly, bond surfaces were produced by silk-screening techniques with metal-containing pastes and burn-in of these pastes, which results in rough surfaces. Together with the ceramic portion of these printed bond surfaces, the adhesion strength of bond wires or of bumps bonded thereon is reduced. The result is that either the mounting speed is reduced or deficiencies with regard to the durability of the resultant bond connection have to be taken into account.